Rotary actuator and method of controlling an actuator

ABSTRACT

A piezoelectric drive body is secured to a shaft that is rotatably supported by a holder. A leaf spring is fastened to the upper end of the holder and is in resilient contact with the upper end of the shaft. Friction between the shaft and the leaf spring acts as a rotation-suppressing force on the shaft. When a sawtooth-waveform voltage is applied to the drive body, the drive body vibrates to the right and left. The drive body rotates around the shaft in a specific direction, due to the difference in inertial force resulting from the difference in the deforming speed of the body. The voltage linearly rises and falls repeatedly or has a sinusoidal waveform. In either case, the voltage rises from a minimum to a maximum for time T 1  and falls from the maximum to the minimum for time T 2  that is different from time T 1 .

This application is a divisional application of application Ser. No.10/245,339, filed Sep. 18, 2002 now U.S. Pat No. 6,676,129.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a rotary actuator having a drive bodythat is rotated around its rotation axis. More particularly, theinvention relates to a technique that is useful when applied to wipersfor cars, outdoor monitor cameras, and meters such as speedometers. Thisinvention also relates to a method of controlling an actuator that isdriven by the vibration of an electromechanical transducer such as apiezoelectric element. More particularly, the invention relates to amethod of controlling an actuator that can reduce the noise the actuatormakes when the input voltage changes.

2. Description of Related Art

Hitherto, a rod-shaped member such as a wiper blade is driven to wipe aglass pane, and a rod-shaped member such as the pointer of a meter or ahand of a clock is driven to indicate a numerical value. Generally,wipers, meters and clocks use rotary actuators driven by electromagneticmotors or hydraulic or air pressure. Electromagnetic motors and the likeare considerably large. Due to their sizes, their design andinstallation are limited. For example, it is desired that a small CCDcamera be equipped with a wiper to clean the front of the camera, but awiper with a motor or an actuator cannot be used because it decreasesthe view field of the camera and occupies a large space. Mostconventional drive mechanisms comprising an electromagnetic motor or thelike require a decelerator, a link and the like, besides theelectromagnetic motor or the like. Inevitably, the drive mechanism tendsto be massive and heavy, and has problems concerning space and weight.The manufacturing cost of the drive mechanism is high, due to its sizeand weight.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a rotary actuator thathas a simple structure, not having an electromagnetic motor or the like,and can yet drive a rod-shaped member. Another object of the inventionis to decrease the noise that the actuator generates while operating.

To attain these objects, an actuator according to this inventioncomprises a drive body having at least one part which vibrates; a shaftmember on which the drive body is mounted; a bearing section supportingthe shaft member and allowing the shaft member to rotate; and aresistance member for applying a rotation-suppressing force to the shaftmember to suppress rotation of the shaft member. As the drive bodyvibrates, the shaft member supported by the bearing section rotates. Thedrive body rotates or oscillates. Basically, the drive body rotates,though the actuator has a simple structure, comprising only four parts,i.e., the drive body, the shaft member, the bearing section and therotation-suppressing member. Having neither an electromagnetic motor nora link mechanism, the actuator in which a drive body formed as arod-shaped member or the like rotates can be small and light. Since aposition to mount the actuator is not restricted by a motor or link, theapparatus layout can be improved. The actuator can be provided in anarrow and small space.

In the actuator, the rotation-suppressing member may apply therotation-suppressing force in the form of a frictional force. If this isthe case, the rotation-suppressing member may be provided at the bearingsection. Alternatively, the rotation-suppressing member may be a leafspring set in resilient contact with the shaft member. The leaf springmay be set in resilient contact with an end portion or a side of theshaft member. The rotation-suppressing member may be provided on theshaft member. The rotation-suppressing member may be an engagement stripset in resilient contact with the bearing section.

Moreover, the drive body may be, for example, a piezoelectric element ofbimorph type. In this case, a voltage having a sawtooth waveform may beapplied to the drive body.

Further, the shaft member may have a hollow extending in its axialdirection, and a wire may extend through the hollow to supply electricpower to the drive body. The drive body may be provided in the form of aplurality of bodies that are secured to the shaft member.

A wiper apparatus according to this invention comprises a wiper blade tobe placed on a wipe surface. The wiper blade has a drive body thatvibrates at least one part. The wiper apparatus also includes a shaftmember on which the wiper blade is mounted. The wiper apparatus furtherincludes a bearing section for supporting the shaft member and allowingthe shaft member to rotate. A resistance member is also included forapplying a rotation-suppressing force to the shaft member to suppressthe rotation of the shaft member. As the drive body vibrates, the wiperblade supported by the bearing section rotates, and the wiper bladerotates or oscillates. The wiper apparatus can therefore be small andlight without using an electromagnetic motor and a link mechanism. Sincea position to mount the actuator is not restricted by a motor or link,the apparatus layout can be improved. The actuator can be provided in anarrow and small space.

The wiper apparatus may be configured to be arranged at the front of aCCD camera. If used in such a manner, the apparatus may be incorporatedin a wiper unit that is attachable to the front of the CCD camera.Further, the wiper apparatus may be applied to a CCD camera mounted on acar.

An indicator according to this invention comprises a pointer composed ofa drive body having at least one part which vibrates. The indicator alsoincludes a shaft member on which the pointer is mounted, and a bearingsection for supporting the shaft member and allowing the shaft member torotate. The indicator further includes a resistance member for applyinga rotation-suppressing force to the shaft member to suppress rotation ofthe shaft member. As the drive body vibrates, the pointer supported bythe bearing section rotates, and the pointer rotates or oscillates. Theindicator can therefore be small and light without using anelectromagnetic motor. The drive body may be attached to the pointer,not formed integral with the pointer. Moreover, the drive body, not thepointer, may be fastened to the shaft member. In this case, the pointeris secured to the drive body.

The indicator may be a speedometer in which the pointer indicates aspeed of a car. In this case, the indicator may further comprise asensor for detecting a position of the pointer.

A motor according to the present invention comprises a drive body havingat least one part which vibrates. The motor also includes a shaft memberon which the drive body is mounted, and a bearing section for supportingthe shaft member and allowing the shaft member to rotate. The motorfurther includes a resistance member for applying a rotation-suppressingforce to the shaft member to suppress rotation of the shaft member. Inthe motor of the invention, as the drive body vibrates, the shaft memberrotates in a predetermined direction. The drive body may be apiezoelectric element of bimorph type. The section that applies a driveforce to the shaft member can be light. The motor can therefore be smalland light, have a small inertia and can quickly respond to the inputpower.

According to the invention there is provided a method of controlling anactuator which is driven by a vibration of an electromechanicaltransducer generated by a change of a voltage applied to theelectromechanical transducer. The applied voltage rises linearly from aminimum value to a maximum value for time T₁, and falls linearly fromthe maximum value to the minimum value for time T₂ that is differentfrom time T₁. The voltage may change along a curve near the maximumvalue and the minimum value.

According to this invention there is provided a method of controlling anactuator which is driven by a vibration of an electromechanicaltransducer generated by a change of a voltage applied to theelectromechanical transducer. The applied voltage has a sinusoidalwaveform, rises from a minimum value to a maximum value for time T₁, andfalls from the maximum value to the minimum value for time T₂ that isdifferent from time T₁.

In this method, the voltage has a linear waveform which the time T₁ isdifferent from the time T₂, or a sinusoidal waveform applied to theelectromechanical transducer. In either case, a difference in thedeforming speed of the transducer can be acquired, a force large enoughto drive the actuator can be generated, and a rapid change of thevoltage can be mitigated. Therefore, the operation noise can be greatlyreduced without reducing the force for driving the actuator, andquietness of the actuator can be improved.

In a method of controlling an actuator which is driven by vibration ofan electromechanical transducer generated by a change of a voltageapplied to the electromechanical transducer, the voltage applied to theelectromechanical transducer has a trapezoidal waveform and remains at aminimum value for a predetermined time and at a maximum value for apredetermined time. In this method, the voltage may change along a curveat both ends of the upper and lower sides of the trapezoidal waveform.Further, the voltage having the trapezoidal waveform may rise from aminimum value to a maximum value for time T₁ and fall from the maximumvalue to the minimum value for time T₂ that is different from time T₁.When the voltage having this waveform is applied to theelectromechanical transducer, the change of the voltage can be mitigatedand the noise that the actuator makes while operating can decrease,because the peaks of the voltage are not sharp edges.

The voltage may rise from a minimum value to a maximum value for time T₁and may fall from the maximum value to the minimum value for time T₂,said time T₁ and said time T₂ having a ratio T₁:T₂ ranging from0.95:0.05 to 0.8:0.2 or ranging from 0.05:0.95 to 0.2:0.8. The operationnoise of the actuator can be reduced while sufficient force to drive it.

According to the present invention there is provided a method ofcontrolling an actuator which is driven by vibration of anelectromechanical transducer generated by a change of a voltage appliedto the electromechanical transducer. The voltage changes along a curvenear a maximum value and a minimum value. Namely, the voltage gentlychanges near the maximum and minimum values, and can remain at eitherpeak for some time. The peaks of the voltage are not sharp edges, whichreduces the noise the actuator makes while operating.

Moreover, the electromechanical transducer used in the method ofcontrolling the actuator, described above, may be a piezoelectricelement of bimorph type made of piezoelectric ceramic.

The above-described and other objects, and novel features of the presentinvention will become more fully apparent from the following descriptionof the following specification in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are schematic representations of the basic structure ofan actuator according to the present invention;

FIG. 2 is a perspective view of a rotary actuator according to anembodiment of this invention;

FIG. 3 is a perspective view illustrating a structure for imparting aforce that suppresses the rotation of the actuator shown in FIG. 2;

FIG. 4 is a side view showing another structure for imparting aresistance to the rotation of the actuator shown in FIG. 2;

FIG. 5 is a side view for explaining a power-supplying system used inthe actuator of FIG. 2;

FIG. 6 is a diagram showing the waveform of a voltage applied to theactuator illustrated in FIG. 2;

FIG. 7 is a diagram illustrating how a drive body operates in theactuator when the voltage shown in FIG. 6 is applied to the actuator;

FIG. 8 is a partly cutaway, perspective view of a wiper, or a secondembodiment of the invention, which incorporates the actuator illustratedin FIG. 2;

FIG. 9A is a front view of a speedometer, or a third embodiment of theinvention, which comprises the actuator of FIG. 2;

FIG. 9B is a sectional view of the speedometer, showing a pointer of thespeedometer;

FIG. 10 is a sectional view of a motor, or a fourth embodiment of theinvention, to which the actuator of FIG. 2 is applied;

FIG. 11A is a plan view of a rotary actuator that is a fifth embodimentof the invention;

FIG. 11B is a front view of the rotary actuator shown in FIG. 11A;

FIG. 12 is a diagram explaining how the rotary actuator operates whenthe voltage shown in FIG. 6 is applied to the rotary actuator;

FIG. 13 is a perspective view of a rotary actuator that is a sixthembodiment of the present invention;

FIG. 14 is a diagram representing the waveform of a voltage applied in amethod of controlling an actuator, which method is a seventh embodimentof this invention;

FIG. 15 is a diagram showing the waveform of a voltage applied in amethod of controlling an actuator, which method is an eighth embodimentof the invention;

FIG. 16 is a diagram showing the waveform of a voltage that may beapplied in place of the voltage illustrated in FIG. 15;

FIG. 17 is a diagram displaying the waveform of a voltage applied in amethod of controlling an actuator, which method is a ninth embodiment ofthe present invention;

FIG. 18 is a diagram displaying the waveform of a voltage applied in amethod of controlling an actuator, which method is a tenth embodiment ofthe invention; and

FIG. 19 is a diagram showing the waveform of a voltage that may beapplied in place of the voltage shown in FIG. 18.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described, with referenceto the accompanying drawings.

First Embodiment

As shown in FIGS. 1A and 1B, the actuator according to the presentinvention comprises a drive body 1, a shaft (shaft member) 2, and abearing section 3. The drive body 1 is shaped like a flat plate. Theshaft 2 holds the drive body 1. The bearing section 3 supports the shaft2. The drive body 1 is a bimorph piezoelectric element that is anelectromechanical transducer. A driver 5 applies a voltage to the drivebody 1 through a wire 4. When applied with the voltage, the drive body 1bends around its proximal end that is coupled to the shaft 2. The distalend of the drive member 1 therefore moves in the direction of arrow X.The bearing section 3 supports the shaft 2, allowing the shaft 2 torotate. A force that suppresses the rotation is imparted to the shaft 2.The rotation-suppressing force is imparted in the form of, for example,a frictional force. The frictional force is generated by a leaf spring13 in the actuator of FIG. 2.

In the actuator 11 shown in FIG. 2, the shaft 2 that holds the drivebody 1 is secured to a holder 12. The holder 12 performs the function ofthe bearing section 3 shown in FIGS. 1A and 1B. That is, it supports theshaft 2, allowing the shaft 2 to rotate. In the actuator 11, the drivebody 1 is a piezoelectric element that is 20 mm long and 3 mm high, andthe shaft 2 has a diameter of 4 mm.

The holder 12 holds a leaf spring (resistance member) 13 at the upperend. The leaf spring 13 applies a frictional force to the top (end) ofthe shaft 2, thus exerting a rotation-suppressing force. As will bespecified later, the rotation-suppressing force applied to the shaft 2is essential to the operation of this actuator 11. In other words, howto generate a stable rotation-suppressing force is important. Togenerate the rotation-suppressing force, a screw may be set in contactwith the shaft. In this case, the screw may be rotated to adjust therotation-suppressing force. This method using a screw can adjust theforce, but an adjustable range is small in amount, thus failing to givea stable rotation-suppressing force. In the actuator 11, the leaf spring13 exerts a rotation-suppressing force on the shaft 2. The leaf spring13 generates an appropriate and stable load on the shaft 2. That is, therotation-suppressing force is stable.

A setscrew 24 fastens the leaf spring 13 to the holder 12. The leafspring 13 has an engagement hole 14 in the tip. A small-diameter portion15 formed at the upper end portion of the shaft 2 is held in the hole14. The stepped part of the shaft 2, defined at the upper end thereof,abuts on the lower surface of the leaf spring 13 resiliently. The leafspring 13 therefore applies the rotation-suppressing force to the shaft2. Thus, a simple and compact mechanism can keep exerting a stable loadon the shaft 2, or applying a stable rotation-suppressing force to theshaft 2.

The shaft 2 and the bearing section 3 cooperate to impart arotation-suppressing force in the actuator 11. The shaft 2 and thesection 3 are indispensable components. They can constitute a structurefor generating a rotation-suppressing force, without requiring othercomponents specialized in suppressing the rotation. Since this structureis provided at the shaft 2, it can be sealed and free of dust when theactuator is applied to, for example, a wiper. This can stabilize thecoefficient of friction between the shaft 2 and the leaf spring 13,whereby the rotation-suppressing force is stable.

The leaf spring 13 may be set in a resilient contact with the side ofthe shaft 2 as is illustrated in FIG. 3. More precisely, the shaft 2 hasa small-diameter portion 16 and a flange 17 and the holder 12 has arecess 18. The flange 17 is placed on the upper surface of the holder12, with the small-diameter portion 16 loosely set in the recess 18.Further, a leaf spring 19 is arranged, covering the opening of therecess 18 and set in a resilient contact with the small-diameter portion16, whereby a rotation-suppressing force is applied to the shaft 2.

The means of applying the rotation-suppressing force may be arranged onthe shaft 2, not on the bearing section 3 as has been described above.As FIG. 4 shows, clip-shaped engagement strips 20 may be provided at thetip of the shaft 2. The engagement strips 20 are fitted in theengagement hole 21 made in the bearing section 3 to obtain frictionalforce. That is, the tip of the shaft 2 is split into four resilientstrips 20, which are bent and inserted into the engagement hole 21. Thetips of the strips 20 protrude from the lower end of the engagement hole21 and are set in resilient contact with the lower surface of thebearing section 3. The strips 20 return resiliently and the outercircumferences thereof also resiliently contact the surface of theengagement hole 21. Friction is thereby generated between the strips 20and the engagement hole 21. Thus, a rotation-suppressing force isapplied to the shaft 2.

FIG. 5 is a side view for explaining the power-supplying system used inthe actuator illustrated in FIG. 2. The shaft 2 of the actuator 11 is ahollow shaft having an axial hole 23. As FIG. 5 shows, a wire 4 extendsthrough the hole 23, for supplying electric power to the drive body 1.In the actuator 11, the wire is not provided outside the drive body 1.Rather, the wire 4 is incorporated in the device. Therefore, the wire 4is not wound around the drive body 1 as the drive body 1 is rotated,though it is slightly twisted. The wire 4 is not damaged. The wire 4 canbe smoothly guided into the interior of the device. In addition, theelectrical system can be waterproof because the wire 4 is not exposed.

The actuator 11 may be applied with a voltage having a sawtooth waveformas shown in FIG. 6. When driven by the voltage, the actuator 11 rotatesaround the axis of the shaft 2. FIG. 6 is a diagram showing the waveformof the voltage applied to the actuator. FIG. 7 is a diagram illustratinghow the drive body 1 operates in the actuator when the voltage shown inFIG. 6 is applied to the actuator. The drive body 1 rotates to the rightin FIG. 7 when the voltage is in the positive phase (+) and to the leftwhen the voltage is in the negative phase (−).

The voltage applied to the actuator changes as illustrated in FIG. 6.When the voltage is at value 1, or ±0, the drive body 1 is at theneutral position P₀. When the voltage rises to a positive value 2, thedrive body 1 rotates to the right as shown in FIG. 7 (1→2). When thevoltage then falls to a negative value 3, the drive body 1 rotates tothe left as indicated in FIG. 7 (2→3).

Since the voltage rapidly changes (2→3), the deforming speed of thedrive body 1 when the voltage falls (2→3) is different from that of whenthe voltage rises slowly as (1→2). In other words, the drive body 1slowly bends every time the voltage rises (1→2) and quickly bends everytime the voltage falls (2→3). Hence, the drive body 1 acquires aninertial force, the force when the voltage falls (2→3) is greater thanthat of when the voltage rises (1→2) because of the difference in thedeforming speed of the drive body 1.

The rotation-suppressing force applied to the shaft 2 acts on theinertial force. The inertial force and the frictional force act againsteach other as the drive body 1 is deformed. In the actuator 11, therotation-suppressing force Fr is set to be larger than the inertialforce F₁₂ when the voltage rises (1→2) and smaller than the inertialforce F₂₃ when the voltage falls (2→3). That is, F₁₂<Fr<F₂₃. Hence, therotation-suppressing force Fr cancels out the inertial force F₁₂generated when the voltage rises (1→2), whereby the drive body 1 slowlyrotates by the angle corresponding to the voltage. By contrast, therotation-suppressing force Fr does not cancel out the inertial force F₂₃generated when the voltage falls (2→3). In this case, the drive body 1rapidly rotates in the opposite direction as the voltage changes, butcannot rotate by such a large angle corresponding to the voltage andcannot return to the initial position.

That is, when the voltage falls (2→3), the inertia of the drive body 1acts more than when the voltage rises, and the drive body 1 rotates lessto the left than it rotates to the right when the voltage rises (1→2).The drive body 1 therefore rotates to the right by a difference betweenthe leftward rotation angle and the rightward rotation angle. In FIG. 7,line Q indicates the axis of the drive body 1 that has rotated to theright and then to the left. As seen from the cases (2→3) and (4→5), lineQ rotates to the right as the drive body 1 rotates to the right (Q₁→Q₂).Dotted, dashed line P₀ shown in FIG. 7 represents the position (i.e.,initial position) that the drive body 1 takes in the case 1 shown inFIG. 7.

As FIG. 6 shows, the voltage of sawtooth waveform gradually rises fromvalue 3 to value 4 after it sharply falls from value 2 to value 3. As aresult, the drive body 1 rotates to the right as is illustrated in FIG.7 (3→4). In this case, the voltage rises at a low rate and the inertiaof the drive body 1 works is small. The drive body 1 rotates to theright by an angle that corresponds to the voltage. When the voltagereaches value 4 (FIG. 6), it rapidly falls again to value 5. At thistime, too, an inertial force is generated from the difference in thedeforming speed of the drive body 1. The angle by which the drive body 1rotates to the left as the voltage changes from value 4 to value 5 (FIG.7) is smaller than the angle by which the drive body 1 rotates to theright as the voltage changes from value 3 to value 4 (FIG. 7). Hence,the drive body 1 rotates to the right by the difference in angle, andline Q also rotates to the right.

When the voltage of sawtooth-waveform is applied, the drive body 1gradually rotates to the right as shown in FIG. 7, due to the inertialforce generated from the difference in the deforming speed of the drivebody 1. Thus, the drive body 1 rotates counterclockwise (see the motionof line Q). Namely, the drive body 1 is slowly bent and quicklystraightened, repeatedly. The drive body 1 self-rotates in the directionin which it is slowly bent. If the voltage gradually falls and quicklyrises, in the mode opposite to the mode shown in FIG. 6, the drive body1 rotates clockwise as is illustrated in FIG. 7. Thus, the drive body 1can be moved back and forth by switching the mode of changing thevoltage. The actuator can therefore oscillate without having a motor ora link mechanism.

The actuator 11 is simple in structure. Nonetheless, the drive body 1can be rotated in the actuator 11. Neither an electromagnetic motor nora link mechanism is required to drive the drive body 1. The actuatorrotating a rod-shaped member can be small and light. Having no motor andno link, the actuator can be laid out anywhere. The actuator thatrotates any component can be installed in a small space.

Second Embodiment

The second embodiment of this invention will be described. The secondembodiment is a wiper for use on CCD cameras, which incorporates theactuator 11 shown in FIG. 2. FIG. 8 is a partly cutaway, perspectiveview of the wiper 31. Hereinafter, the mutually corresponding members,parts, etc. in the first embodiment are designated by the same referencenumerals and a detailed description is omitted for simplicity.

Recently, CCD cameras have found use in cars so that the drivers may seeother cars and pedestrians approaching at blind crossroads or T-roads,without necessity of driving the cars deep into the crossroads orT-roads. In such a car, some CCD cameras are secured to the side bumpersor provided behind the front grills, respectively. The display providedin the car displays the left and right images that the CCD cameras haveoutput. When it rains, however, rain drops stick to the front pane ofeither CCD camera. Consequently, the images generated by the CCD camerasdo not provide adequate view fields. To give a sufficiently large viewfield to the camera, a wiper may be attached to the front of either CCDcamera. In the past this could not be achieved, however, because aconventional wiper has a motor for driving the wiper blade and isinevitably too large to be attached to the front of a CCD camera, whichis small.

The wiper 31 according to the invention, which incorporates an actuator,needs no motor whatsoever, and the wiper can be small enough to be usedwith the CCD camera. As seen from FIG. 8, the wiper 31 comprises a cover32 and the actuator 11 of FIG. 2, which is secured to the cover 32. Thewiper 31 can be attached to the front of a CCD camera 33 as a wiper unitintegrated with the cover 32. The wiper 31 can be set in the front ofthe CCD camera 33 without additional work to the body thereof.

A rubber blade 34 is fastened to the drive body 1 of the actuator 11 andfunctions as wiper blade 35. The wiper blade 35 can oscillate around theshaft 2, on the glass surface 36 (wipe surface) of the CCD camera 33.When the driver (not shown) applies a voltage to the drive body 1, thewiper blade 35 oscillates on the glass surface 36, removing raindropsand dust from the surface 36.

The wiper 31 need not comprise an electromagnetic motor or a linkmechanism to drive the blade. It can therefore be small and light. Sincethe motor and the link do not restrict a blade position, the apparatuslayout can be improved and the wiper can be provided in a narrow andsmall space. It can be attached to not only CCD cameras for cars, butalso any devices and positions which are relatively small and which havenot hitherto been provided with wipers.

The wiper 31 incorporates the actuator 11 illustrated in FIG. 2.Nonetheless, it may have an actuator of the structure shown in FIG. 3.If the rubber blade 34 generates a rotation-suppressing force, the wiper31 need not comprise the leaf spring 13.

Third Embodiment

The third embodiment of the present invention will be described. Thethird embodiment is a speedometer that incorporates the actuator IIshown in FIG. 2. FIGS. 9A and 9B show the speedometer 41. FIG. 9A is afront view, and FIG. 9B is a sectional view of the speedometer, showinga pointer of the speedometer.

As illustrated in FIGS. 9A and 9B, the drive body 1 of the actuator 11is used as the pointer 42 of the speedometer 41. That is, the pointer 42is made of a piezoelectric element. The pointer 42 is fixed to the shaft2 that protrudes from the meter panel 43 of the speedometer 41. Thebearing section 3 of the actuator 11, which is shaped like a ring, isprovided on the back of the meter panel 43. The bearing section 3supports the shaft 2, allowing the same to rotate. The shaft 2 has beenslightly pressed into the bearing section 3, so that the section 3 mayapply a rotation-suppressing force to the shaft 2. In this embodiment,the bearing section 3 works as a friction member.

A sensor disk 44 is fastened to the lower end of the shaft 2. The sensordisk 44 has a plurality of magnetic poles that are arranged in thecircumferential direction of the disk 44. A rotation sensor 45 (sensorfor detecting the position of the pointer) is located near the sensordisk 44. The rotation sensor 45 detects the position to which thepointer 42 rotates when electric power is supplied to the drive body 1.More precisely, the rotation sensor 45 detects the change of themagnetic poles as the sensor plate 44 rotates, to thereby measure theangle through which the sensor disk 44 rotates.

When the driver 5 applies the voltage that corresponds to the speed ofthe car to the drive body 1, the pointer 42 rotates around the shaft 2over the panel 43. The rotation sensor 45 detects the rotation angle ofthe pointer 42, and the drive body 1 is controlled based on the detectedangle to move the pointer 42 to the right position.

The pointer drive mechanism can be provided in the space accommodatingthe pointer in the speedometer 41. Further, no electromagnetic motorneeds to be used to drive the pointer 42. The speedometer 41 can besmall and light. The speedometer 41 therefore has an increased freedomof layout. The pointer 42 can be secured to the shaft 2, merely by beingmounted on the shaft 2 protruded from the panel 43. This enhances theefficiency of assembly of the speedometer 41. The shaft 2 may be of thetype illustrated in FIG. 4. In this case, the shaft 2 may only beinserted into the bearing section 3 fixed to the back of the meter panel43.

Instead of the pointer 42 being the drive body 1, a pointer made ofsynthetic resin or metal may be secured to the drive body 1. Thestructure of the third embodiment can be applied to meters other than aspeedometer and a clock that have pointers. When the driver 5 stopsapplying the voltage to the drive body 1, the pointer 42 is held inposition, due to the rotation-suppressing force. In view of this, thethird embodiment is desirable as a meter that is designed to measure aphysical amount that changes very little or as a meter whose pointer canbe stopped whenever desired. To measure the speed, the speedometer 41does not need electric power at all times, which saves power.

Fourth Embodiment

The fourth embodiment of this invention will be described. The fourthembodiment is a motor that incorporates the actuator 11 shown in FIG. 2.FIG. 10 shows the motor 51. The actuator 11 can not only swing a wiper,but also work as a rotary machine, and it can form the motor 51 shown inFIG. 10.

In the motor 51, two drive bodies 1 are mounted on the shaft 2. Bothdrive bodies 1 are provided in a housing 52 that is placed on a baseplate 53. A ball bearing 54 (bearing section) is fitted in the baseplate 53. A metal bearing 55 is fitted in the top wall of the housing52. The bearings 54 and 55 support the shaft 2, allowing the shaft 2 torotate. The shaft 2 is slightly pressed into the metal bearing 55.Therefore, the metal bearing 55 applies a rotation-suppressing force tothe shaft 2.

The shaft 2 is a hollow one. A wire 4 extends through the hole 23, forsupplying electric power to the drive body 1. The wire 4 is connected toslip rings 56 that are mounted on the upper end portion of the shaft 2.The slip rings 56 are contained in a case 57 that is mounted on the topof the housing 52. The driver 5 applies a voltage to the drive bodies 1through the slip rings 56.

When the driver 5 applies a voltage of a sawtooth waveform to the motor51, the drive bodies 1 move as shown in FIG. 7 and rotate the shaft 2 inany direction desired. The output torque of the shaft 2 can becontrolled by changing the voltage applied to the drive bodies 1.Further, the speed of the shaft 2 (number of rotations per unit time)can be adjusted by changing the frequency of the sawtooth voltage.Furthermore, the output torque can be controlled by changing the numberof drive bodies 1. For example, the slip ring 56 is provided for eachdrive body 1, and the number of drive bodies 1 with voltage appliedthereto may be changed, to thereby change the output of the motor 51.

In the motor 51, the drive bodies 1 are bimorph piezoelectric elementsand drive the shaft 2. The section that imparts a drive force to theshaft 2 can be of a small weight. The motor 51 can therefore be smalland light, can have small inertia, and can yet respond well to the inputpower.

The number of drive bodies 1 used is not limited to two. The motor 51may have only one drive body. Alternatively, the motor 51 may have threeor more drive bodies to increase its output. The means for generating arotation-suppressing force may be a leaf spring or a rubber plate set insliding contact with the shaft 2. The slip rings 56 may be replaced byany other components that can supply power to the drive bodies 1. Theymay be replaced by, for example, commutators.

Fifth Embodiment

The fifth embodiment of the invention will be described. The fifthembodiment is a rotary actuator in which the free end of a drive body isloosely held and the shaft secured to the fixed end of the drive body isrotated. FIGS. 11A and 11B show the rotary actuator 101, i.e., the fifthembodiment of the invention. FIG. 11A is a plan view, and FIG. 11B afront view. FIG. 12 is a diagram explaining how the rotary actuator 101operates.

As FIGS. 11A and 11B show, the actuator 101 comprises a drive body 102,a bearing section (first shaft member) 103, a shaft (second shaftmember) 104, and a support section 105. The drive body 102 is shapedlike a plate; it is a bimorph piezoelectric element as in the firstembodiment. The bearing section 103 holds the proximal end of the drivebody 102. The shaft 104 is secured to the bearing section 103. Thesupport section 105 supports the drive body 102. A driver applies avoltage to the drive body 102 through a wire (not shown). When thevoltage is applied to the drive body 102, the drive body 102 is bent, inits entirety except the proximal end, around the bearing section 103,and its distal end portion acts in the same way as in the firstembodiment.

A force is exerted on the shaft 104 to suppress the rotation of theshaft 104. More specifically, the shaft 104 has clip-shaped engagementstrips of the type shown in FIG. 4. The engagement strips are fitted inthe hole made in the bearing section 103. A friction develops betweenthe strips and the hole. The friction suppresses the rotation of theshaft 104.

The drive body 102 has its proximal end held by the support section 105that is mounted on a base 106. The support section 105 is made ofelastic material such as rubber or foamed plastic. It supports one endof the drive body 102 such that the drive body 102 and the bearingsection 103 can vibrate but will not touch the base 106 located belowthe drive body 102 and the bearing section 103. The drive body 102 canmove up and down (FIG. 11A) in the support section 105.

The actuator 101 may be applied with a voltage having such a sawtoothwaveform as shown in FIG. 6. When driven by the voltage, the actuator101 rotates around the axis of the shaft 104. As shown in FIG. 12, thedrive body 102 rotates to the right when the voltage is in the positivephase (+) and to the left when the voltage is in the negative phase (−).More precisely, the drive body 102 is at the initial position P₀ whenthe voltage has value 1 in FIG. 6, or 0 volt. When the voltage rises tovalue 2, a positive value, as shown in FIG. 6, the drive body 102 movesto the right (112, in FIG. 12). Then, when the voltage falls from value2 to value 3, a negative value, as shown in FIG. 6, the drive body 102moves to the left (2→3, in FIG. 12). In FIG. 12, the support section 105holding the distal end of the drive body 102 is not shown, in order toclearly demonstrate the motion of the drive body 102. In the supportsection 105, actual displacement of the drive body 102 is only 0.1 mm orless. The drive body 102 repeatedly moves in the support section 105.

As indicated earlier, the drive body 102 is deformed at a rate whilemoving to the right (1→2, in FIG. 12), and at a different rate whilemoving to the left (2→3, in FIG. 12). The drive body 102 has an inertialforce due to its weight and tends to remain where it is located. Theinertial force the body 102 has while moving to the left (2→3) isgreater than the inertial force it has while moving to the right (1→2),due to the difference in terms of the deforming speed of the drive body102. A reaction to the inertial force is generated at the bearingsection 103. The reaction, i.e., a force for rotating the body 102, isgreater while the body 102 is moving to the left (2→3) than while thebody 102 is moving to the right (1→2).

The rotation-suppressing force Fr, i.e., the friction between thebearing section 103 and the shaft 104, acts against the force forrotating the drive body 102. The force Fr is larger than theshaft-rotating force F₁₂ acting while the body 102 is moving to theright (1→2) and is smaller than shaft-rotating force F₂₃ acting whilethe body 102 is moving to the left (2→3). Thus, F₁₂<Fr<F₂₃. While thebody 102 is moving to the right (1→2), the bearing section 103 and theshaft 104 rotate clockwise together, with virtually no slipping betweenthem, because force F₁₂ acting clockwise is smaller than therotation-suppressing force Fr. While the body 102 is moving to the left(2→3), the bearing section 103 and the shaft 104 slip on each otherbecause force F₂₃ is larger than the rotation-suppressing force Fr. Inthis case, the shaft 104 can hardly rotate counterclockwise. Therefore,the drive body 102 remains deformed in the direction it has rotated(1→2), and the shaft 104 rotates clockwise. Note that the body 102rotates in the direction opposite to the direction it rotates as shownin FIG. 7. This is because the bearing supporting the drive body 102rotates, not the drive body as in the case shown in FIG. 7.

The voltage of sawtooth waveform rapidly falls from value 2 to value 3as shown in FIG. 6. It then gradually rises from value 3 to value 4,i.e., a positive value. The drive body 102 therefore moves to the right(3→4, in FIG. 12) as the voltage changes. As the body 102 moves so, aforce is generated at the bearing section 103 to rotate the drive body102, reacting to the inertial force exerted on the drive body 102.Nonetheless, the force for rotating the body 102 is small as in the case(1→2), since the voltage changes at a low rate. Hence, the shaft 104rotates clockwise together with the bearing section 103 as the voltagechanges.

After the voltage rises to value 4 (FIG. 6), it rapidly falls to value5. In this case, too, the drive body 102 acquires an inertial force dueto the difference in the deforming speed of the drive body 102. Areaction to the inertial force is generated, acting as a large force forrotating the drive body 102. Therefore, the bearing section 103 and theshaft 104 slip on each other as in the case (2→3), and the shaft 104scarcely rotates counterclockwise. In other words, the shaft 104 doesnot rotate counterclockwise as indicated by broken lines in the cases(2→3) and (4→5), though it rotates clockwise as indicated by solid linesin the cases (1→2) and (3→4). After all, the shaft 104 rotates clockwiseas the voltage changes from value 1 to value 5.

When the voltage of sawtooth waveform is applied to the drive body 102,the shaft 104 gradually rotates clockwise as shown in FIG. 12, due tothe inertial force generated from the difference in the deforming speedof the drive body 102. In this case, too, the shaft 104 can be rotatedin the forward direction or the reverse direction by switching thepattern of changing the voltage. The number of times the shaft 104rotates per unit time can be controlled by changing the frequency of thesawtooth-waveform voltage. Further, the torque of the shaft 104 can becontrolled by changing the voltage.

The actuator 101 is composed of four components (i.e., drive body 102,bearing section 103, shaft 104 and support section 105). It is simple instructure. The shaft 104 can yet be driven at a low speed and a hightorque. Neither an electromagnetic motor nor a multi-phase,high-frequency power supply is required to drive the shaft 104. Theactuator 101 can, therefore, be a small, light and inexpensive rotaryactuator. Since the actuator 101 is thin, it has a high freedom oflayout. The actuator 101 can be laid out in a narrow and small space.

Sixth Embodiment

The sixth embodiment of the invention will be described. The sixthembodiment is a rotary actuator. FIG. 13 is a perspective view of therotary actuator. The mutually corresponding members, parts, etc. in thefifth embodiment are designated by the same reference numerals and willnot be described.

In an actuator 121 of FIG. 13, a drive body 102 is arranged in thevertical direction. The drive body 102 is held by a support section 105that is fastened to a bracket 106. The bracket 106 is a metal memberthat has an L-shaped cross section. Its horizontal part 106 a is securedto the upper surface of a base 122. The vertical part 106 b of thebracket 106 holds a holding plate 123. The inner side of the plate 123is lined with a foamed plastic layer 124. The drive body 102 is securedto the support section 105, with its lower end held by the foamedplastic layer 124. The drive body 102 is adhered to the foamed plasticlayer 124 with an adhesive tape or the like. Having its lower end heldby the foamed plastic layer 124, the drive body 102 can vibrate, thoughit is fixed to the support section 105.

In the actuator 121, the shaft 104 is attached to the upper end of thedrive body 102. A bearing section 103 is mounted on a shaft 104 and canrotate relative to the shaft 104. A disc 125 is secured to the bearingsection 103. The shaft 104 and the bearing section 103 perform the samefunction as the first and second shafts of the fifth embodiment,respectively. That is, the shaft and the bearing section areinterchangeable in position in the fifth and sixth embodiments. Whetherthe shaft 104 or the bearing section 103 is fastened to the drive body102 and acts as the output-side part is nothing more than a designchoice.

A rotation-suppressing force is applied to the bearing section 103. Inthe fifth embodiment, a rotation-suppressing force is exerted on theshaft 104. In the sixth embodiment, the force is exerted on the bearingsection 103. Namely, whether the bearing section 103 or the shaft 104receives the rotation-suppressing force depends on which componentfunctions as the output-side part. In other words, a force is applied tosuppress the relative rotation between the bearing section 103 and theshaft 104 in both the fifth embodiment and the sixth embodiment. Theshaft 104 is made of phosphor bronze. It has clip-shaped engagementstrips as in the fifth embodiment. The bearing section 103 is made offluorocarbon resin and is set in elastic engagement with the engagementstrips of the shaft 104. The friction between the engagement strips, onthe one hand, and the bearing section 103, on the other, suppresses therotation of the bearing section 103.

Such a sawtooth-waveform voltage as shown in FIG. 6 is applied to theactuator 121. The disc 125 fastened to the bearing section 103 rotatesdue to the relation between the rotation-sustaining force and the forceon the shaft 104, which is a reaction to the inertial force that hasbeen generated from a change in the voltage as described earlier. Thedisc 125 can be rotated in the forward direction and the reversedirection, by switching the mode of changing the voltage. In addition,the rotational speed of the disc 125 can be controlled by changing thefrequency of the sawtooth-waveform voltage, and the rotation torque ofthe disc 125 can be controlled by changing the voltage.

Both actuators 101 and 121 can drive not only a driven member by thebearing section 103 directly as in the sixth embodiment, but also drivethe blades of car wipers, the pointers of speedmeters, and the hands ofclocks by securing a rod-shaped member to the bearing section 103 or theshaft 104.

Seventh Embodiment

The seventh embodiment of this invention will be described. The seventhembodiment is a method of controlling the actuator 11 according to thefirst embodiment. FIG. 14 is a diagram representing the waveform of avoltage applied to the actuator 11.

If such a sawtooth-waveform voltage as illustrated in FIG. 6 is appliedto the piezoelectric element, a problem will arise. A noise will begenerated when the voltage applied rapidly falls from value 2 to value 3or from value 4 to value 5 as is shown in FIG. 6. People near theactuator may recognize this noise as an annoying one. It is thereforeimportant to minimize the noise.

In the seventh embodiment, a voltage having such a waveform as shown inFIG. 14 is applied to prevent a noise. As seen from FIG. 14, the voltageapplied to the actuator 11 has a frequency of 250 Hz and changes betweenthe maximum and minimum values that differ by 200V. The voltage risesfrom the minimum value to the maximum value over time T₁ and falls fromthe maximum value to the minimum value over time T₂. Time T₁ and time T₂differ from each other; T₁:T₂=0.8:0.2. Applied with the voltage havingthis specific waveform, the drive body 1 rotates to the right while thevoltage has a positive (+) value and to the left while the voltage has anegative (−) value, as is illustrated in FIGS. 6 and 7.

Since the voltage changes as shown in FIG. 14, the drive body 1 bendsthrough an angle proportional to the voltage, regardless of the rate atwhich the voltage changes. Assume that the drive body 1 slowly bendsthrough +10° with respect to the shaft 2 when it is applied with +100V.Then, the shaft 2 is held and will not slip, because of therotation-suppressing force. Its distal end portion bends through +10° asin the case of a cantilever. When the drive body 1 is applied with −100Vand is thereby rapidly bent in the opposite direction, its distal endportion cannot bend as much as −10° due to the inertial force explainedabove. Although the drive body 1 tends to rotate by the anglecorresponding to the voltage, its distal end portion cannot so much. Asa result, the shaft 2 supporting the drive body 1 overcomes therotation-suppressing force and slips in the direction opposite to thedirection in which the distal end portion of the body 1 bends. Namely,the shaft 2 rotates.

Thus, the shaft 2 slips due to the inertial force generated from thedifference in the deforming speed of the drive body 1, when the voltageof the waveform shown in FIG. 14 is applied to the drive body 1. Thedistal end of the drive body 1 therefore gradually rotates to the rightas it slips, whereby the drive body 1 rotates counterclockwise. If thevoltage falls more slowly than it rises, lengthening time T₂ andshortening time T₁, or if T₁:T₂=0.2:0.8, for example, the drive body 1will rotate to the left (clockwise) in FIG. 7.

When the voltage having such a waveform as shown in FIG. 14 is appliedto the drive body 1, it is possible to impart a sufficient difference inthe deforming speed of the body 1 and to generate a force large enoughto drive the body 1, provided that time T₁ and time T₂ are set at anappropriate ratio. Thus, this control method can greatly reduce thenoise and quietness of the actuator can be improved, without decreasingthe drive force much. The experiments conducted by the inventors hereofdemonstrated that when the voltage having the waveform shown in FIG. 14was applied, the noise was reduced to about 45 dB from about 65 dB,i.e., the value observed when the sawtooth-waveform voltage (FIG. 6) wasapplied.

Eighth Embodiment

The eighth embodiment of the invention will be described. The eighthembodiment is a method of controlling the actuator 11 according to thefirst embodiment by applying a voltage that slowly changes near themaximum and minimum values (turning values), not sharply as isillustrated in FIG. 14. FIG. 15 is a diagram representing the waveformof the voltage applied to the actuator 11 in this method.

As FIG. 15 displays, the waveform of the voltage has a curvilinear part61 at the positive (+) peak and the negative (−) peak. In other words,neither peak is a sharp edge. The voltage gradually changes at eachpeak. This helps to minimize the noise that the actuator 11 makes whenthe input voltage changes.

The noise reduction is effective to a sawtooth-waveform voltage as shownin FIG. 16. FIG. 16 is a diagram showing a modified form of the waveformshown in FIG. 15, which is corresponding to the case that the time T₂ is0 (T₂=0) in FIG. 15. Although, the voltage rapidly falls from themaximum value to the minimum value, sharp edges are removed near thepeaks by the curve 61. Since the voltage slowly changes at each peak,the noise that actuator 11 makes while operating is small.

Ninth Embodiment

The ninth embodiment of this invention will be described. The ninthembodiment is a method of controlling the actuator 11 by applying avoltage having a sinusoidal waveform, which changes in magnitude andpolarity with time. FIG. 17 is a diagram displaying the waveform of thevoltage applied to the actuator 11 in this method.

As FIG. 17 shows, a voltage of a sinusoidal waveform has a frequency of250 Hz and a potential difference of 200V between the maximum andminimum values. For this voltage, T₁:T₂=0.8:0.2. When applied with thevoltage having this waveform, the drive body 1 moves as shown in FIG. 7,rotating clockwise around the shaft 2. Therefore, the drive body 1generates a sufficient force for the actuator, and the operation noisecan yet be small since the voltage does not change so rapidly.

Tenth Embodiment

The tenth embodiment of this invention will be described. The tenthembodiment is a method of controlling the actuator 11 by applying avoltage having a trapezoidal waveform. FIG. 18 is a diagram displayingthe waveform of the voltage applied to the actuator 11 in this method.

As FIG. 18 shows, a voltage of a trapezoidal waveform, the maximum andminimum values of which remain unchanged for a specific time (T₃). Thetime T₁, during which the voltage rises from the minimum value to themaximum value is different from the time T₂ during which the voltagefalls from the maximum value to the minimum value-, as indicated above.That is, T₁:T₂=0.8:0.2. When applied with the voltage having thiswaveform, too, the drive body 1 moves as shown in FIG. 7. Nonetheless,the peaks of the voltage are not sharp edges; the voltage remains at themaximum and minimum values for some time (T₃).

As shown in FIG. 19, a voltage having the curvilinear part 61 may beapplied to the drive body 1. The voltage roundly changes near the peaksin the curvilinear part 61. Also, it is possible to make the curvilinearpart 61 at both an upper base 62 and a lower base 63 on the trapezoidalwaveform shown in FIG. 18. The voltage having a trapezoidal waveform canserve to reduce the noise because it changes gently at the peaks, evenif T₂=0. The positive peak 62 and negative peak 63 of the trapezoidalwaveform may be a curve or a zigzag wave.

A detailed description has hereinabove been given of the inventionachieved by the present inventors with reference to the embodiments.However, the present invention should not be limited to the embodimentsdescribed above, and may be variously modified within the scope notdeparting from the gist.

For example, the rotation-suppressing force is applied in the form of africtional force in the embodiments described above. Instead, therotation-suppressing force may be applied by a magnetic brake or anelectromagnetic brake. If the force is a frictional force, its source isnot limited to a leaf spring. A coil spring, a rubber ring or the like,either mounted on or provided in the shaft, may be used to apply therotation-suppressing force. Further, the leaf spring may be providedoutside the actuator, not at the bearing section as in the embodiments.For example, the leaf spring 13 may be secured to the cover 32 in thecase of the wiper 31.

Moreover, the drive body 1 need not vibrate in its entirety, so long asit can move as is illustrated in FIG. 7. The drive body 1 may beconfigured to vibrate at its distal portion only. The dimensionsspecified of the drive body 1 are nothing more than an example. The body1 may have any other dimensions.

In the embodiments described above, the ratio between the rising time T₁and falling time T₂ of the voltage is: T₁:T₂=0.8:0.2. The ratio is notlimited to this, nevertheless. To reduce the noise, while generating asufficient drive force in the actuator, the ratio is preferably:T₁:T₂=0.95:0.05 to 0.8:0.2 (T₁:T₂=0.05:0.95 to 0.2:0.8, to drive theactuator in the opposite direction). A bimorph piezoelectric element isemployed as the electromechanical transducer in the embodiments, but anyother transducer, such as a quartz element, may be utilized instead. Avoltage whose polarity changes with time is applied to the actuator 11in the above embodiments. Nonetheless, a voltage that changes butremains positive or negative, not changing in polarity, may be appliedto drive the actuator 11.

1. A method of controlling an actuator having a drive body whichincludes an electromechanical transducer that is operable to vibratewhen a change of a voltage is applied thereto, a shaft member on whichsaid drive body is mounted, a bearing section for supporting said shaftmember and allowing said shaft member to rotate, and a resistance memberfor applying a rotation-suppressing force to said shaft member tosuppress rotation of said shaft member, the method comprising: applyinga voltage to said electromechanical transducer such that the voltageincreases linearly from a minimum value to a maximum value for a time T1and decreases linearly from the maximum value to the minimum value for atime T2 that is different than the time T1.
 2. The method of claim 1,wherein the voltage is applied so that the voltage changes along a curvenear the maximum value and along a curve near the minimum value.
 3. Themethod of claim 1, wherein the time T1 and the time T2 have a ratioT1:T2 ranging from 0.95:0.05 to 0.8:0.2.
 4. The method of claim 1,wherein the time T1 and the time T2 have a ratio T1:T2 ranging from0.05:0.95 to 0.2:0.8.
 5. The method of claim 1, wherein saidelectromechanical transducer is a piezoelectric element.
 6. A method ofcontrolling an actuator having a drive body which includes anelectromechanical transducer that is operable to vibrate when a changeof a voltage is applied thereto, a shaft member on which said drive bodyis mounted, a bearing section for supporting said shaft member andallowing said shaft member to rotate, and a resistance member forapplying a rotation-suppressing force to said shaft member to suppressrotation of said shaft member, the method comprising: applying a voltageto said electromechanical transducer such that the voltage increasesfrom a minimum value to a maximum value for a time T1 and decreases fromthe maximum value to the minimum value for a time T2 that is differentthan the time T1, wherein the voltage has a sinusoidal waveform.
 7. Themethod of claim 6, wherein the time T1 and the time T2 have a ratioT1:T2 ranging from 0.95:0.05 to 0.8:0.2.
 8. The method of claim 6,wherein the time T1 and the time T2 have a ratio T1:T2 ranging from0.05:0.95 to 0.2:0.8.
 9. The method of claim 6, wherein saidelectromechanical transducer is a piezoelectric element.
 10. A method ofcontrolling an actuator having a drive body which includes anelectromechanical transducer that is operable to vibrate when a changeof a voltage is applied thereto, a shaft member on which said drive bodyis mounted, a bearing section for supporting said shaft member andallowing said shaft member to rotate, and a resistance member forapplying a rotation-suppressing force to said shaft member to suppressrotation of said shaft member, the method comprising: applying a voltageto said electromechanical transducer, the voltage having a trapezoidalwaveform remaining at a minimum value for a predetermined time andremaining at a maximum value for a predetermined time.
 11. The method ofclaim 10, wherein the voltage changes along a curve at both ends of theupper and lower sides of the trapezoidal waveform.
 12. The method ofclaim 10, wherein the voltage increases from the minimum value to themaximum value during a time T1 and decreases from the maximum value tothe minimum value during a time T2 that is different than the time T1.13. The method of claim 12, wherein the time T1 and the time T2 have aratio T1:T2 ranging from 0.95:0.05 to 0.8:0.2.
 14. The method of claim12, wherein the time T1 and the time T2 have a ratio T1:T2 ranging from0.05:0.95 to 0.2:0.8.
 15. The method of claim 12, wherein saidelectromechanical transducer is a piezoelectric element.
 16. The methodof claim 10, wherein said electromechanical transducer is apiezoelectric element.
 17. A method of controlling an actuator having adrive body which includes an electromechanical transducer that isoperable to vibrate when a change of a voltage is applied thereto, ashaft member on which said drive body is mounted, a bearing section forsupporting said shaft member and allowing said shaft member to rotate,and a resistance member for applying a rotation-suppressing force tosaid shaft member to suppress rotation of said shaft member, the methodcomprising: applying a voltage to said electromechanical transducer, thevoltage changing along a curve near a maximum value and along a curvenear a minimum value.